10 research outputs found
Experimental observation of the optical spin-orbit torque
Spin polarized carriers electrically injected into a magnet from an external
polarizer can exert a spin transfer torque (STT) on the magnetization. The phe-
nomenon belongs to the area of spintronics research focusing on manipulating
magnetic moments by electric fields and is the basis of the emerging
technologies for scalable magnetoresistive random access memories. In our
previous work we have reported experimental observation of the optical
counterpart of STT in which a circularly polarized pump laser pulse acts as the
external polarizer, allowing to study and utilize the phenomenon on several
orders of magnitude shorter timescales than in the electric current induced
STT. Recently it has been theoretically proposed and experimentally
demonstrated that in the absence of an external polarizer, carriers in a magnet
under applied electric field can develop a non-equilibrium spin polarization
due to the relativistic spin-orbit coupling, resulting in a current induced
spin-orbit torque (SOT) acting on the magnetization. In this paper we report
the observation of the optical counterpart of SOT. At picosecond time-scales,
we detect excitations of magnetization of a ferromagnetic semiconductor
(Ga,Mn)As which are independent of the polarization of the pump laser pulses
and are induced by non-equilibrium spin-orbit coupled photo-holes.Comment: 4 figure, supplementary information. arXiv admin note: text overlap
with arXiv:1101.104
Direct measurement of the three dimensional magnetization vector trajectory in GaMnAs by a magneto-optical pump-and-probe method
We report on a quantitative experimental determination of the
three-dimensional magnetization vector trajectory in GaMnAs by means of the
static and time-resolved pump-and-probe magneto-optical measurements. The
experiments are performed in a normal incidence geometry and the time evolution
of the magnetization vector is obtained without any numerical modeling of
magnetization dynamics. Our experimental method utilizes different polarization
dependences of the polar Kerr effect and magnetic linear dichroism to
disentangle the pump-induced out-of-plane and in-plane motions of
magnetization, respectively. We demonstrate that the method is sensitive enough
to allow for the determination of small angle excitations of the magnetization
in GaMnAs. The method is readily applicable to other magnetic materials with
sufficiently strong circular and linear magneto-optical effects.Comment: main paper: 7 pages, 3 figures; supplementary information: 11 pages,
6 figure
Light-Induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As
Precession of magnetization induced by laser pulses in (Ga,Mn)As was studied by the pump-and-probe technique. We concentrated on various experimental aspects that can be used to identify a part of the measured magneto-optical signals that provides information about the dynamics of magnetization. We also revealed that that it takes about 80 ps before the quasi-equilibrium precession of magnetization is initiated by the impact of laser pulse